1. Field of the Invention
The present invention relates to a ceramic body and a ceramic catalyst body used as a catalyst support in an exhaust gas purifying catalyst of an automobile engine, or the like.
2. Description of the Related Art
Cordierite that has high durability against thermal shock has been widely used as a ceramic body for a catalyst support. The catalyst is made by applying a γ-alumina coating on the surface of cordierite that is formed in honeycomb shape, and providing it with a noble metal catalyst supported thereon. The coating layer is formed because the specific surface area of the cordierite is too small to support a required amount of catalyst component. Thus surface area of the support is increased by using γ-alumina that has a large specific surface area.
When the surface of the support is coated with γ-alumina, however, the heat capacity of the carrier increases due to the increase in the mass. Recently, investigations have been conducted for means to make the heat capacity smaller by making the cell wall of the honeycomb support thinner, in order to achieve earlier activation of the catalyst. However, the effect of this attempt is reduced by the formation of the coating layer. There have also been such problems that the coefficient of thermal expansion of the support becomes larger due to the coating layer, and the decrease in the opening area of the cell increases the pressure loss.
Various researches have been conducted to achieve ceramic bodies capable of supporting catalyst components without forming a coating layer. In Japanese Examined Patent Publication (Kokoku) No. 5-50338, for example, such a method is proposed that improves the specific surface area of cordierite itself by applying heat treatment after pickling. However, this method has not been practical because a pickling process or a heat treatment causes the destruction of the crystal lattice of cordierite, thus resulting in lower mechanical strength.